Definitely excited Kiseki is getting more love. I figure the massive potential spoilers are slightly offset by the fact that nobody purchasing the books should be surprised considering that they're about five games (the Crossbell-centric cover art being a bit of a giveaway). The OVA marketing is pretty deceptive (or you could be charitable and just assume Sentai had morons involved in the marketing of the thing) but Udon has basically said straight up to expect coverage of unlocalized games.
There's no spoiler issue here because anyone concerned about spoilers know it goes without saying. I'm conflicted because this is something I should support and would probably enjoy flipping through a few times over, but I've never shelled out for an art book before. What do you do with it? It's not your standard coffee table book. I'd like to think the best art is all at our fingertips with a few quick searches, maybe throwing Falcom Collections into the mix.
Go to Gamestop, buy a Steam card, and use it to purchase Ys Origin. You won't be disappointed. Don't reboot PCs that you cannot access.
I'm thinking of doing a spoiler-free summary of the contents later tonight, to quantify things for anyone who's curious. For availability, some of the art is certainly easy to find online (or in other books not up for translation) but these two put most of it in one place and nicely organize it. There's also a fair bit that's exclusive to the books.